In France, I have the same 3 months period where I still have to work. If they decide to lock my computer during this period, I'm free to stop working and tell them to provide me with a new computer ASAP since I cannot do anything at all.

Unless they want to fire you and then they still could remove those 3 months and give you some money instead. It would be stupid of them to give me a free salary for 3 months: either they fire me properly, or they give me a computer.